The disclosure relates generally to turbomachines, and more particularly, to a turbine airfoil having a near wall, trailing edge cooling circuit formed in a cover and allowing coolant recycling.
Gas turbine systems are one example of turbomachines widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor section, a combustor section, and a turbine section. During operation of a gas turbine system, various components in the system, such as turbine blades and nozzle/vane airfoils, are subjected to high temperature flows, which can cause the components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of a gas turbine system, it is advantageous to cool the components that are subjected to high temperature flows to allow the gas turbine system to operate at increased temperatures.
A multi-wall rotating blade or stationary nozzle typically contains an intricate maze of internal cooling passages. Cooling air provided by, for example, a compressor of a gas turbine system, may be passed through and out of the cooling passages to cool various portions of the multi-wall blade. Cooling circuits formed by one or more cooling passages in a multi-wall blade/nozzle may include, for example, internal near wall cooling circuits, internal central cooling circuits, tip cooling circuits, and cooling circuits adjacent the leading and trailing edges of the multi-wall blade. In order to cool a tip of a trailing edge of a turbine airfoil and because the trailing edge provides very little internal space for defining a cooling circuit, coolant for the trailing edge is typically delivered in one or both of the following ways. In one approach, the airfoils include a coolant passage(s) that delivers a coolant through and out of the trailing edge, and in another approach, coolant is delivered out a side of the airfoil and across an exterior surface immediately upstream of the tip of the leading edge. In either approach, the coolant is delivered only in a single, downstream direction out to the hot gas path of the turbine. Once the coolant leaves the airfoil it is lost and cannot be recycled for cooling other parts.